Ask those doing the building.

Ask your architect.

Eight feet does seem a bit narrow. Ask your builder/architect if you can do some form of cantilever, like this:

If the deck goes to the building envelope (I assume you mean the setback?), I doubt you can extend it, even with a cantilever, without getting a variance in the building permit. This is not impossible, and adding 2' would make a much more functional deck.

In my city, a cantilever cannot extend more than 1/4 the length of the deck, so 2' would be the max.

thanks Ann - I do mean the building envelope. Our lot is a bit odd as it has 2 building envelopes where any structures must reside inside of them (one for home and one is for pool currently). I think they had the deck posts go to the edge of the envelope which takes the deck to 8 feet. I had not thought about the cantilever option but my assumption is as long as the posts supporting hte deck are inside the envelope it should be fine with a cantilever

Do not build a new home on assumptions. These restrictions, whether HOA or zoning generated, are best dealt with by someone with intimate knowledge of the written restrictions and their purpose. They can be complex and misinterpreted easily by anyone.

I couldn't agree more about assumptions, Mark!

I am in the process of building a deck, and the inspections department has been good about answering questions. Your local building code is probably available on line, and could also be helpful.

A "building envelope" is usually what is created by the exterior walls. If you are talking about a zoning sideyard setback, the ordinance should specify whether or not it applies to an open deck or a covered deck but if it apples to this deck, it almost certainly applies equally to the footings, posts and deck.